Harnessing Platelet-Endothelial Interactions for Exosome Delivery

PROJECT SUMMARY Studies have demonstrated that adult stem cells such as mesenchymal stem cells (MSCs) repair myocardial infarction (MI) or ischemia/reperfusion (I/R) injury by indirect paracrine mechanisms rather than by differentiation and tissue replacement. In the past decade, exosomes have emerged as promising cell-free agents for treating ischemic injury. Several exosome-based therapeutic companies have launched early phase clinical trials. Like most therapeutics, there is an urgent need for effective delivery strategy to ensure a sufficient number of exosomes to reach the injured tissue. Since they are nanosized natural lipid bilayer particles, one option is vascular delivery. However, high and repeated dosing is needed due to a large degree of off-target distribution to the mononuclear phagocyte system and other organs, such as the liver, spleen and lungs. Moreover, MSC-derived exosomes (MSC-XOs) need to compete with naturally existing exosomes in body fluids. Cellular binding and uptake of MSC-XOs also hinder the therapeutic effects. Novel approaches are required to deliver therapeutic exosomes to cells in injured tissues. Ideally, modified exosomes should 1) reduce the clearance by the mononuclear phagocyte system, 2) bind to injured blood vessels, and 3) be efficiently uptake by target cell types in injured tissues. It has been established that acute MI can induce vascular damage and expose components of the subendothelial matrix including collagen, fibronectin and von Willebrand factor (vWF) to recruit platelets. Platelets can bind to and accumulate on injured vasculature following MI. Instead of generically modifying the parental cells or chemically engineering exosomes, we used platelet membranes to envelope exosomes (to make P-XOs) and increase their macropinocytosis-mediated cellular internalization, and their ability to target the injured tissue. In this proposed study, we plan to investigate the fabrication, characterization and toxicity of P-XOs (AIM 1). After that, we will test the therapeutic effect of P-XOs on a mouse model (AIM 2) and a porcine model (AIM 3) with cardiac injury. Our study will provide new insights on cellular internalization mechanism of exosomes, targeting properties and mechanism of the P-XOs treatment. Together, the proposed mechanistic and translational experiments will provide a scientific premise to understand system administrated exosomes while suggesting new approaches for promoting targeting and therapeutic effect of therapeutic exosomes.